1. Field of the Invention
The present invention relates to radio-frequency identification (RFID) markers for detection of surgical implements; and more particularly, to use of an RFID marker embedded in or otherwise securely attached to a surgical implement, such as a laparotomy pad or sponge, metallic surgical instrument, or other implement, for preventing the inadvertent retention of such implement during a surgical procedure.
2. Description of the Prior Art
Many patents disclose methods for detection of surgical implements following surgery prior to wound closure. Such detection methods incorporate x-ray opaque markers within surgical implements and effect detection using postoperative x-ray of the patient or of discarded sponges. Also disclosed as being suitable for detection of surgical implements are methods involving use of resonant tags made from magnetomechanical elements, capacitors, LRC oscillatory circuits and smart markers.
U.S. Pat. Nos. 4,114,601 and 4,193,405 to Abels disclose a medical and surgical implement detection system. Surgical implements such as metallic instruments, sponges, implantable devices and indwelling therapeutic devices and materials are detected within the human body or other area of interest by incorporating or adding a radio-frequency transponder. A microwave system mixes two fundamental microwaves having 4.5-5 GHZ frequencies and relies on a non-linear transponder to produce higher order product frequencies. The transponder may be a thin film of a ferrite material exhibiting gyro-magnetic resonance at selected frequencies or a solid-state device containing diodes and field effect transistors. A non-linear transponder signal is received by a receiving antenna and filtered to remove all fundamental microwave frequencies. Unfortunately, substantially all of the higher order microwave frequencies generated by the transponder are readily absorbed by the human body. Consequently, most higher order microwave frequency signals are lost before any non-linear transponder can be detected. In addition, the gyro-magnetic effect produces a relatively weak signal.
U.S. Pat. No. 4,658,818 to Miller, Jr., et al. discloses an apparatus for tagging and detecting surgical implements. A miniature battery-powered oscillator is attached to each surgical implement and activated prior to its initial use. The output of each oscillator has the form of a low powered pulse of 1-10 MHZ frequency, and is coupled to the body's fluids and tissue. Following surgery but prior to suturing, a detection system senses for any pulses generated by the oscillator within the body. The surgical implement detection system disclosed by the '818 patent is not passive. It requires a miniature battery, which is turned on at the beginning of the operation. When the operation is complete, the battery may have already discharged, in which event the surgical implement will not be detected by the apparatus.
U.S. Pat. No. 5,057,095 to Fabian discloses a surgical implement detector utilizing a resonant marker for use in human or animal tissue. The marker is triggered into resonance by the interrogating field. A resonance frequency signal emitted by the marker is detected by a separate detection circuit adjacent to the interrogating circuit. The marker resonates due to magnetostriction properties of an amorphous metal ribbon, a piezoelectric device or a tuned LRC circuit. The response from the marker constitutes a simple sine wave having a particular frequency, which is less than one gigahertz. A detector is responsive within an interrogation zone encompassing a surgical wound. The marker is adapted to undergo resonance solely at a pre-selected frequency below 1 GHz, causing a substantial change in its effective impedance. An electromagnetic dipole field is thereby generated, which produces an identifying signal identity. The interrogation means is also provided with a means for varying phase and/or direction of the interrogating field. A receiving means placed within the interrogation zone detects the “ring-down”, phase-shift, impedance or other identifying characteristic of the element in resonance.
U.S. Pat. No. 5,188,126 to Fabian, et al. discloses a surgical implement detection system utilizing capacitive coupling for use in human or animal tissue. The system comprises a battery-powered marker, which is secured to the surgical implement and positioned within a surgical wound. A detection means has an antenna disposed in close proximity to the tissue. Means are provided for capacitance coupling of the marker with the antenna and activation of the battery-powered marker. A field generating means associated with the detection system generates an electromagnetic field having a predetermined frequency band ranging from about 10 MHz to 1 GHz. The electromagnetic field causes the marker to produce a signal in the form of a sinusoidal wave having unique signal identity. A battery powers the capacitive marker, which will not function when the battery is discharged. Inasmuch as there is no means to verify the status of the battery, this method for detection of surgical implements is vulnerable to battery failure.
U.S. Pat. No. 5,190,059 to Fabian, et al. discloses a surgical implement detector utilizing a powered marker for use in human or animal tissue. A battery-powered marker is secured to a surgical implement positioned within the wound. An electromagnetic field generating structure in the battery-powered marker is provided for generating within the transmitting zone an electromagnetic field having a predetermined frequency band, providing the marker with signal identity. The response from the battery-powered marker is a simple sine wave having a particular frequency. Such a response does not comprise a digital code; it lacks the capacity for identifying a surgical implement. Battery power is required; detection is not effected when the battery is discharged.
U.S. Pat. No. 5,329,944 to Fabian, et al. discloses a surgical implement detector having an acoustic marker appointed for use within animal or human tissue. The acoustic marker is battery powered and is retained in a watertight case. The marker produces an identifying acoustic signal with pre-determined frequency characteristics within the wound. The detector may be a stethoscope. The battery-powered acoustic marker runs constantly. When the battery runs down, the battery-powered acoustic marker stops emitting its characteristic acoustic frequency. This event may occur before all the surgical implements have been removed from the surgical wound, adversely affecting the marker's reliability.
U.S. Pat. No. 5,541,604 to Meier discloses transponders, interrogators, systems and methods for elimination of interrogator synchronization requirement. A Radio-frequency Identification (RFID) system has an interrogator and a transponder, the interrogator having a first tuned circuit of a powering frequency for sending a powering burst to a transponder, a filter/demodulator for receiving a wireless, modulated RF response from a transponder. The interrogator additionally has a second tuned circuit in electrical communication with a modulator. The second tuned circuit has a selected bandwidth about a communication frequency. The selected bandwidth does not substantially overlap the powering frequency and encompasses the bandwidth of the modulated carrier of the RF response. The carrier is modulated using pulse width modulation (PWM), pulse position modulation (PPM), frequency-shift keying modulation (FSK), or another type of modulation methods. The interrogator also has a controller in electrical communication with the filter/demodulator and the tuned circuits. It enables the first tuned circuit to send the powering burst during a first time period and enables the modulator in electrical communication with the second tuned circuit to receive the RF response during a second time period. The transponder has a tuned circuit. A tuning circuit in electrical communication with the tuned circuit modifies the frequency characteristics of the tuned circuit. The circuit is thereby tuned during the powering burst to the powering frequency. It is also tuned during the RF response to the communication frequency. The transponder also includes a demodulator in electrical communication with the tuned circuit for receiving the RF interrogation therefrom and for demodulating data from the RF interrogation. This current generation RFID device sends a preset code to the interrogator. It is powered entirely by the power burst signal provided in the first time period and is capable of transmitting the code at a high rate to the interrogator.
U.S. Pat. No. 5,664,582 to Szymaitis discloses a method for detecting, distinguishing and counting objects. A marker made from a nonmagnetostrictive strip of amorphous or crystalline material produces higher harmonic excitations when energized by an alternating magnetic field. The higher harmonics are detected by the exciting antenna. This passive, non battery-powered device receives a fixed second harmonic frequency sinusoidal signal based on the size, shape and material of the marker. Information is not digitally encoded and therefore the marker has no means for identifying individual counting objects.
U.S. Pat. No. 5,931,824 to Stewart, et al. discloses an identification and accountability system for surgical sponges and includes machine-readable information located on a plurality of surgical sponges used in the surgical procedure. At the end of an operation the surgical implements are machine read to determine whether any of the sponges are missing. The system also includes an x-ray detector for the detection of missing sponges. Detection of sponges placed within a surgical wound is not effected unless the absence of a sponge is detected during the sponge count procedure following surgery. Actual location of a missing sponge requires x-ray examination.
U.S. Pat. No. 6,026,818 to Blair, et al. discloses a tag and detection device. An inexpensive tag has the form of a ferrite bead with a coil and a capacitor, or a tag of flexible thread composed of a single loop wire and capacitor element. The detection device locates the tag by pulsed emission of a wide band transmission signal. The tag resonates with a radiated signal, in response to the wide band transmission. Resonation occurs at the tag's own single, non-predetermined frequency, within the wide band range. The pulsing action of the wide band transmission builds the non-predetermined, radiated signal intensity over the ambient noise levels. This radiated signal is a sinusoidal wave of non-predetermined frequency and does not have digital information that identifies a particular sponge or surgical pad.
U.S. Pat. No. 6,076,007 to England, et al. discloses surgical devices and their location. A surgical device, such as a catheter or a prosthesis, carries, at a predetermined location, a tag composed of a high permeability, low coercivity magnetic material having a magnetized bias element. The tag is interrogated with a rotating magnetic field. Interaction between the tag and the rotating magnetic field is detected by a flying null system to determine the location of the tag within the human or animal body. Typically, the marker will be in the form of a thin film, a wire or a strip. The response signal from the tag is a sinusoidal wave with no digital information. The detection system is based on flying null technology. The tag is used for locating a catheter tip, not a sponge or surgical pad within a surgical wound.
U.S. Pat. No. 6,424,262 and US Patent Application No. 20040201479 to Garber, et al. disclose applications for radio-frequency identification systems. An RFID target is used, together with magnetic security element and a bar code reader, to check out and manage library materials such as reference books, periodicals, and magnetic and optical media. This disclosure has nothing to do with detecting sponges or surgical pads in a surgical wound.
U.S. Pat. No. 6,838,990 to Dimmer discloses a system for an excitation leadless miniature marker. An excitation field excites a leadless marker assembly. The system comprises a source generator assembly having a power supply, an energy storage device, a switching network and an untuned source coil interconnected and configured to deliver a selected magnetic excitation signal waveform, such as continuous bipolar or unipolar waveform, or a pulsed magnetic excitation signal waveform. The power supply is configured to deliver power to energize the energy storage device. The switching network is configured to: direct electrical current through the source coil. It alternately switches between a first on position and a second on position. Stored energy is alternately transferred from the energy storage device to the source coil and from the source coil back to the energy storage device. The source coil is coupled to the switching network to generate an excitation signal. Untuned excitation is used by the source coil to look for resonance from a set of markers embedded in human tissue. Information is processed using an array sensor to three-dimensionally locate a given marker. This system does not locate sponges or surgical pads misplaced in a surgical cavity. The frequency response of a target is sinusoidal and has no digital capability.
US Patent Application No. 2002/0143320 to Levin discloses tracking medical products with integrated circuits. Radio-frequency identification devices comprising a microprocessor, memory, analog front end and antenna are used to communicate with a remote unit. The remote unit has a processor memory and transreceiver that receives digital data from radio-frequency identification devices attached to medical products, such as a pharmaceutical product, a blood product or a tissue product. The radio-frequency identification device is first scanned and then rescanned at the end of the surgical procedure. There is no indication that the radio-frequency identification devices are encapsulated. Neither is there any indication that the RFID devices are incorporated in a sponge, surgical pad or surgical implement. Further, there is no indication in the Levin application that the RFID devices are scanned during surgery to establish the location of the sponge or surgical pad. There is also no indication in Levin application that the RFID devices are scanned at the end of an operating procedure to establish that no sponges or surgical pads are left behind in a surgical cavity.
US Patent Application No. 2003/0006878 to Chung discloses a smart tag data encoding method. Information is stored in a smart tag having a memory. The smart tag has two memory portions. One of the partitions is permanent and cannot be erased. A second memory portion stores application specific data. The second memory portion also stores a relational check number, which validates the integrity of the data stored in the second memory, thereby detecting memory alteration or corruption. This smart tag data encoding method has nothing to do with detecting a sponge or surgical pad left behind in a surgical wound.
US Patent Application No. 2003/0057279 to Uozumi et al. discloses an identifying system for an overlapped tag. An RFID and one or more resonance capacitors connected through on-off switches may be turned on or off by a remote control circuit. The overlapping tags may be interrogated using an RFID system, or one more resonance capacitors. The Uozumi et al. system does not detect sponges and surgical pads in a surgical wound, since they are not expected to overlap. Signals from the resonant capacitors of Uozumi et al. form a sine wave comprising electromagnetic radiation and do not carry a digital code
US Patent Application No. 20030066537 to Fabian, et al. discloses a surgical implement detection system. Surgical implements used during an operating procedure are detected in human tissue. Markers attached to the surgical implements change their impedance at a preselected frequency in the presence of an electromagnetic field. The system uses a magnetomechanical element which vibrates at a preselected frequency when excited. This preselected frequency, when detected, indicates the presence of a surgical implement to which the magnetomechanical marker element is attached. The marker resonates only at a fixed frequency and provides no digital information suited for identifying a sponge or a surgical pad.
US Patent Application No. 20030105394 to Fabian, et al. discloses a portable surgical implement detector. Surgical implements used during an operating procedure are detected in human or animal tissue. Markers attached to the surgical implements change their impedance at a preselected frequency in the presence of an electromagnetic field. Each of the markers is thereby provided with signal-identifying characteristics. The portable detector sweeps the surgical cavity with a range of frequencies which excites and vibrates markers attached to surgical implements at preselected frequencies, causing their detection. The markers resonate at preselected frequencies in the form of sinusoidal waves, but do not provide digital data suited for identifying a sponge or surgical pad.
US Patent Application No. 20030192722 to Ballard discloses a system and method of tracking surgical sponges. The sponges have a radiopaque object embedded therein, which is visible when the sponge container is x-rayed. All sponges brought into the operating room are x-ray identified. A missing sponge is detected by this accounting process. The system does not actively detect whether a sponge is accidentally left behind in a surgical wound. The patient is not x-rayed to determine whether the missing sponge is inside the surgical wound.
US Patent Application No. 20040129279 to Fabian, et al. discloses a miniature magnetomechanical tag for detecting surgical sponges and implements. This tag is a magnetomechanical device and is excited by the interrogating magnetic field. The interrogating field is switched off, and the ring down characteristic of the resonant target is detected. The system does not provide digital means for identifying a sponge or surgical pad.
US Patent Application No. 20040250819 to Blair, et al discloses an apparatus and method for detecting objects using tags and a wideband detection device. An apparatus and method for the detection of objects in the work area, such as surgical sites, including a detection tag affixed to objects used during surgery, is disclosed. The apparatus and method feature interrogates with a transmitter emitting a pulsed wideband signal, prompting the tag element to provide a return signal, which is received and analyzed. The device features an antenna portion containing a single or a plural ring-shaped antenna. Also, the pulsed wideband interrogation signal may be pulsed-width modulated or voltage-modulated. The pulsed signals trigger a continuing response signal from the tag in its response frequency range, which increases in intensity to the point where it becomes differentiable from background noise and is detected within the wideband range by the signal detector as an indication of the presence of the tag. The tag is excited by a wide band pulsed interrogation signal, which builds up the output of the tag and can be detected over ambient electronic noise. The tag signal has a predetermined frequency in the form of a sinusoidal wave, and does not carry digital information suitable for identifying laparotomy pads or sponges retained within the wound cavity.
US Patent Application No. 2005/0003757 to Anderson discloses an electromagnetic tracking system and method having a single-coil transmitter. The system includes a single coil transmitter emitting a signal, a receiver receiving a signal from the single coil transmitter, and electronics for processing the signal received by the receiver. The electronics determine a position of the single coil transmitter. The transmitter may be a wireless or wired transmitter. The receiver may be a printed circuit board. The electronics determine position, orientation, and/or gain of the transmitter. The single coil transmitter is a powered device and may be wired or wireless. It is not a passive device that can be incorporated in a sponge or surgical pad due to the requirement for a reliable power source.
PCT Patent Application No. WO 98/30166 to Fabian et al. discloses a surgical implement detector utilizing a smart marker. The surgical implement is appointed for disposition within human or animal tissue and is made to be electronically identifiable by affixing thereto a smart marker, which is an unpowered integrated circuit with EEPROM memory carrying a code. When the smart marker is sufficiently close to the reader antenna, a voltage is generated within the marker antenna that charges the capacitor and powers the integrated circuit. A switch is opened and closed to transmit the stored code in the EEPROM memory, providing identification and recognition of a smart target attached to a surgical sponge. The marker antenna operates at a frequency of near 125 KHz. The frequency of information transfer to the reader is very slow, due to the switching on and off action. Moreover, the smart marker is not encapsulated, and is subject to damage by blood and other saline fluids.
There remains a need in the art for a highly reliable, non battery-powered, surgical implement detection marker that may be attached to laparotomy pads or sponges, metallic and other surgical implements. Also needed is a marker of the type described, which can withstand cleaning and sterilization procedures commonly employed, and resists exposure to body fluids such as blood or saline solutions. A non battery-powered surgical implement marker and corresponding detection device, is needed to provide a reliable indication of the location of foreign objects within a surgical wound during and at the completion of a surgical procedure prior to wound closure